An oscilloscope is a debugging tool for electronics circuits where you can prob any point and check out the signal in watch it in real time (voltage over time)for example you could check an Arduino PWM signal with this tool and measure the duty cycle, voltage or if it is even working at all.I bought minehereThis is a starting level device and it has it's limitation but it is cheap and will do the job.It does not have it's own display like and expensive, portable and professional ones, but it will rather connect to your computer via USB and you will see the signal over the computers screen when lunching the application that comes with it.